Early generation intermating for yield improvement in groundnut (Arachis hypogaea L.)

Summary Seeds of 4 crosses of groundnut (Arachis hypogaea L.), Robut 33-1 x Chico, Robut 33-1 x NC Ac 17090, Robut 33-1 x PI 298115 and MK 374 x GAUG 1, were irradiated with 30 kR. In the F₁, some branches of each plant were intermated with other plants at random and others selfed in each cross to produce S₂ and F₂ seeds. They were evaluated for pod yield, shelling percentage and 100-kernel weight. The frequency of plants superior to F[in1] was much higher in S₂ than in F₂, which was, in general, true for the values of yield and its components. The S₂ and F₂ were advanced to third generation by selfing. The families descending from S₂ showed clear superiority over those from F₂. The reason for such superiority was suggested to be the recombination of genes from the upper and lower ends of the genotypic distribution under intermating.     

Diallel analysis in groundnut (Arachis hypogaea L.)

Summary An 8 × 8 full diallel experiment based on 4 bunch plus 4 spreading types of groundnut (Arachis hypogaea L.) was conducted over three environments. For both number of pods and pod yield, additive, nonadditive and reciprocal cross effects were detected and these were also influenced by changes in environments. For number of pods additive genetic variance was predominant whereas it was approximately equal to non-additive genetic variance for pod yield. Graphical analysis revealed the presence of strong non-allelic interaction for number of pods whereas for pod yield absence of dominance and/or presence of non-allelic interaction was evident.Part of Ph.D. Thesis of the first author     

Inadequate iron supply and high bicarbonate impair the symbiosis of peanuts (Arachis hypogaea L.) with different Bradyrhizobium strains

In the present study, we examined the effects of iron deficiency in an acid solution and in an alkaline solution containing bicarbonate on the growth and nodulation of peanuts inoculated with different bradyrhizobial strains or supplied with fertilizer nitrogen.Inadequate iron supply in acid solution decreased the number of nodule initials, nodule number and nodule mass. Alleviating the iron deficiency increased acetylene reduction but not bacteroid numbers in nodules. Nitrogen concentrations in shoots of inoculated plants increased as iron concentrations in solution increased when determined at day 30 but not at day 50. Higher iron concentrations in solution were required for maximum growth of plants reliant on symbiotic nitrogen fixation than for those receiving fertilizer nitrogen.Adding bicarbonate to the solution with 7.5 M Fe markedly depressed nodule formation. This effect was much more severe than that of inadequate iron supply alone. Bicarbonate also decreased nitrogenase activity but did not decrease bacteroid concentrations in nodules.Both NC92 and TAL1000 nodulated peanuts poorly when bicarbonate was present. However, an interaction between iron concentrations in acid solutions and Bradyrhizobium strains on nodulation of peanuts was observed. Alleviating iron deficiency increased the number of nodule initials and nodules to a much greater extent for plants inoculated with TAL1000 than for plants inoculated with NC92.     

Uptake and partitioning of cadmium by cultivars of peanut (Arachis hypogaea L.)

Cadmium has been found to accumulate in peanut (Arachis hypogaea) kernels to levels exceeding the current maximum permitted concentration in Australia of 0.1 mg kg^-1. Little is known of the mechanisms of Cd uptake into kernels by cultivars of peanut, so the aims of the experiments reported here were to determine if Cd is absorbed directly through the pod wall or via the main root system, and if differences exist between cultivars in this respect. Split-pot soil and sand/nutrient solution experiments were performed with two cultivars of peanut (cv. NC7 and Streeton) known to accumulate Cd to different levels in the kernel. The growth medium was separated into pod and root zones with Cd concentrations in each zone varied. In confirmation of previous field trial results, cv. NC7 had higher concentrations of Cd in kernels, given the same Cd levels in the external medium (solution or soil). Despite total Cd uptake by cv. NC7 being similar to cv. Streeton, cv. NC7 appeared to retain more Cd in the roots and translocate less Cd to shoots. Results from both soil and sand/solution culture indicated that the dominant path of Cd uptake by peanut was via the main root system, with direct pod uptake contributing less than 5% of the total Cd in the kernel. There was little difference between cultivars in this characteristic. This indicates that unlike Ca nutrition of peanuts, agronomic techniques to manage Cd uptake will require modification of soil to the full depth of root exploration, rather than just the surface strata where pods develop. Cadmium concentrations in testa were up to an order of magnitude higher than in the kernel, indicating that blanching of kernels would be effective in reducing Cd in the marketed product. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nodulation and symbiotic nitrogen fixation of cowpea (Vigna unguiculata (L.) Walp)

Summary Rhizobium strains CIAT 301, CIAT 79 and SLM 602 were tested and found effective in the nodulation and nitrogen fixation of cowpea cv. MI-35 (Vigna unguiculata (L.) Walp) plants in growth chamber experiments. Fresh weight of nodules increased with plant age initially and stabilized in 20–30 days from planting, followed by a secondary flush of nodule growth after 30 days. Apparent nitrogen fixation per gram nodule fresh weight reached a maximum in 20–30 days after planting and then decreased, even though a flush of new nodules was produced.     

Enhanced cross pollination to widen the scope of breeding in groundnut (Arachis hypogaea L.)

Summary Six groundnut genotypes belonging to the Virginia and Valencia sub-groups were irradiated with gamma rays at doses of 5, 10, 15 and 20 kR, much below LD₅₀, and grown surrounded by a pollen parent in a split-plot design. The succeeding two generations were checked for the occurrence of hybrids by examining the segregation for pod and seed characteristics and the two quantitative characters, pod and seed yield. Cross-pollination up to 20.8% was observed in M13, a Virginia cultivar. There was a genotype-dose interaction for the extent of cross-pollination. Cross-pollination was higher in Virginia than Valencia genotypes and more frequent under 15 and 20 kR than under other doses, in general. The observed substantial enhancement of cross-pollination encourages the use of seed irradiation at proper doses as a method for increasing recombination in plant breeding programmes.     

Crop residue application increases nitrogen fixation and dry matter production in groundnut (Arachis hypogaea L.) grown on an acid sandy soil in Niger,West Africa

Field experiments were conducted during the rainy reasons of 1989, 1990 and 1991 on an acid sandy soil in Niger, West Africa, to assess the effect of millet straw application (+CR) on growth and N₂ fixation of groundnut (Arachis hypogaea L.).Three years of +CR (4 t ha^–1 yr^–1) increased symbiotic N₂ fixation, total dry matter production (haulm plus pods) by 83% and total nitrogen (N) accumulation by 100%. Concentration of N in the shoot dry matter and total N in the soil were only slightly affected by the +CR treatment.Crop residue application increased the concentration of potassium (K) and molybdenum (Mo) and decreased the concentrations of aluminium (Al) and manganese (Mn) distinctly, both in the plant (shoot and nodule dry matter) and in the soil.The increase in dry matter production and N uptake was mainly due to improved N₂ fixation reflected by enhanced formation and growth of nodules as well as nitrogenase activity. This was attributed to improved chemical soil conditions, particularly to the higher availability of Mo and the lowered content of available Al and Mn.Although with the application of 4 t CR ha^–1, 60 kg K were supplied, increased growth could not be attributed to the additional supply of K.ICRISAT Journal Article No. 1229.ICRISAT Journal Article No. 1229.     

Genetic variation for VA mycorrhiza-dependent phosphate mobilisation in groundnut (Arachis hypogaea L.)

Nine cultivars of groundnut (Arachis hypogaea L.) were grown in a soil poor in available N or P. There was clearly genetic variation of characteristics indicative of VA mycorrhiza-dependent phosphate mobilisation, namely, VA mycorrhiza fungal spore count (SC), percentage of infection (IF) by VA mycorrhizal fungi (VAMF) and acid and alkaline phosphatase activities. Among the cultivars, one was non-nodulating with low values for all characteristics and in another experiment, this non-nodulating cultivar, one of its parents (PI 259747), a national check (Robut 33-1) and the highest yielding cultivar among the original nine (NFG 7), were grown and investigated for various P-mobilising properties and yield. The linear regression coefficient of pod yield on % VAMF infection was significant in both the experiments. Additionally, many of the correlation coefficients of pod yield and VAM dependent characteristics were positive and significant. From consideration of published evidence, it seems possible to breed for the desirable reinforcing effects of infestation, by VAMF and Rhizobium that can ultimately improve the productivity of groundnuts.     

Diversity and compatibility of peanut (Arachis hypogaea L.) bradyrhizobia and their host plants

A high degree of genetic diversity among 125 peanut bradyrhizobial strains and among 32 peanut cultivars collected from different regions of China was revealed by using the amplified fragment length polymorphism (AFLP) technique. Eighteen different peanut bradyrhizobial genotypes and six peanut cultivars were selected for symbiotic cross-inoculation experiments. The genomic diversity was reflected in the symbiotic diversity. The peanut cultivars varied in their ability to nodulate with the strains used. Some cultivars had a more restricted host range than the others. Also the strains displayed a range of nodulation patterns. In yield formation there were clear differences between the plant cultivar/bradyrhizobium combinations. There was good compatibility between some peanut bradyrhizobial strains and selected cultivars, with inoculation resulting in well-nodulated, high-yielding symbiotic combinations, but no plant cultivar was compatible with all strains used. The strains displayed a varying degree of effectiveness, with some strains being fairly effective with all cultivars and others with selected ones. The AFLP genotypes of the strains did not explain the symbiotic behavior, whereas the yield formation of the plant cultivars was more related to the genotype. It is concluded that to obtain optimal nitrogen fixation efficiency of peanut in the field, compatible plant cultivar-bradyrhizobium combinations should be selected either by finding inoculant strains compatible with the plant cultivars used, or plant cultivars compatible with the indigenous bradyrhizobia.     

In vitro flowering and pod formation from cotyledons of groundnut (Arachis hypogaea L.)

Summary The response of groundnut cotyledons to the presence of various growth regulators in concentrations from 0.1 to 5 mg/l has been studied in detail using several genotypes of groundnut on two different media. Cotyledons with embryo axis, cultured on Blaydes' medium with cytokinins, produced shoots, in the axils of which 2–7 flower buds could be seen. The frequency of flower bud induction in general increased with increasing concentrations of cytokinins, the optimal levels being 3 mg/l of KN or 4 mg/l of BAP. Cotyledons without embryo axis, cultured on Blaydes' medium with BAP (0.5 mg/l), produced a cluster of flower buds directly, ranging in number from 8–28, without any vegetative growth. Excised embryo axes cultured on the same medium gave plantlets without flower buds. The growth regulators IAA, NAA, GA₃ and ABA failed to induce flower buds in independent treatments. However, lower concentrations of IAA and NAA in combination with cytokinins exerted a positive influence on flowering. The blooming of the flower buds was facilitated on media supplemented with low concentrations of cytokinins. Six percent of the induced flowers resulted in gynophore development and ultimately formed pods when cultured under complete dark conditions in modified MS medium supplemented with kinetin.     

Efficient selection intensity in early generation index selection in groundnut (Arachis hypogaea L.)

Summary The F₂ potential of single and three-way crosses was evaluated using a set of physiological and yield components. Results were based on an index of selection using (a) only yield components and (b) both physiological and yield components. The indices were constructed using the percentage improvement of F₂ over the better parent of the corresponding F₁ cross for every character. The performance of F₂ plants assessed by the expected value of the regression index was ranked in descending order to provide a ranked F₂ distribution (FRD). The FRD was divided into four equal parts, T₂₅ (top 25%), T₅₀ (26–50%), T₇₅ (51–75%) and T₁₀₀ (76–100%). F₃ families derived from F₂ plants in T₂₅ were found to provide a higher frequency of selections for pod number than T₅₀, T₇₅ and T₁₀₀. The frequency of selections was higher in three-way than single crosses. Selection index based on physiological and yield components was more efficient in trapping F₂ plants providing selections in F₃ than the index based on yield components only. The results brought out the importance of bunch x bunch crosses as a complement to the usually advocated bunch x runner ones.     

Variation and inheritance of the arachin polypeptides of groundnut (Arachis hypogaea L.)

Summary Variation in the arachin polypeptides of groundnut genotypes was observed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Three regions could be observed on the electropherogram. Region 1, corresponding to conarachin, did not show any variation; region 2, consisting of arachin acidic subunits, showed variation; region 3, containing the arachin basic subunits, did not show any variation. There are four varietal classes of arachin polypeptide patterns: class A comprised three acidic subunits of arachin of molecular weights 47.5, 45.1 and 42.6 kd and a basic subunit of 21.4 kd; class B, with three acidic subunits of molecular weights 47.5, 45.1 and 41.2 kd and a basic subunit of 21.4 kd; class C of an additive pattern of class A and class B; class D, of two acidic polypeptides of 47.5, 45.1 kd and the basic 21.4 kd subunit. Of the 90 genotypes studied, 73% belong to class A, 15% to class B and 6% each to class C and D. Analysis of F₂ seeds from a cross between class A and class B genotypes showed that the two polypeptides (42.6 kd and 41.2 kd) are coded by nonallelic genes and also revealed that class C and class D patterns arose as a result of hybridisation between class A and class B. A. monticola, the progenitor of A. hypogaea, showed a pattern similar to the additive pattern of class A and class B while some diploid Arachis species had the 41.2 kd polypeptide. Based on arachin polypeptide patterns the probable origin of A. hypogaea has been suggested.     

The influence of zinc and sulphur deficiency on oil-filling in peanut (Arachis hypogaea L.) kernels

In the developing peanut (Arachis hypogaea L.) kernels, the period between 15 and 35 days after podding (DAP) was identified as the active period of oil-filling. The period of active oil-filling was associated with a decrease in the starch, soluble sugars and proteins so as to make available the energy and carbon skeleton for the synthesis of oil. The oil content in the mature kernels decreased by 11, 12 and 25 per cent with Zn, S and Zn+S deficiency, respectively. In addition, proteins and starch content decreased significantly while that of soluble sugars increased slightly. The activity of malate dehydrogenase and glucose-6-phosphate dehydrogenase also decreased due to Zn as well as S deficiency. The deficiency treatments resulted in a decrease in phospholipids, free fatty acids and triacylglycerols in mature kernels. Further the proportion of 16∶0 and 18∶2 decreased while that of 18∶1 increased in developing kernels.     

Comparative identification by fatty acid analysis of soil,rhizosphere, and geocarposphere bacteria of peanut (Arachis hypogaea L.)

Bacterial isolates were collected from the geocarposphere, rhizosphere, and root-free soil of field grown peanut (Arachis hypogaea L.) at three sample dates, and the isolates were identified by analysis of fatty acid methyl-esters to determine if qualitative differences exist among the bacterial microflora of these zones. Five bacterial genera were associated with isolates from soil, while pod and root isolates constituted 16 and 13 genera, respectively, indicating that bacterial diversity was higher in the rhizosphere and geocarposphere than in soil. The dominant (most frequently identified) genus across all three samples dates was Flavobacterium, for pods, Pseudomonas for roots, and Bacillus, for root-free soil. Sixteen bacterial taxa were only isolated from the geocarposphere, 7 only from the rhizosphere, and 5 only from soil. These results show that specific bacterial taxa are preferentially adapted to colonization of the geocarposphere and suggest that the soil, rhizosphere, and geocarposphere constitute three distinct ecological niches. Bacteria which colonize the geocarposphere should be examined as potential biological control agents for pod-invading fungi such as the toxigenic strains of Aspergillus flavus and A. parasiticus.     

Evaluation of peanut (Arachis hypogaea L.) leaflets from mature zygotic embryos as recipient tissue for biolostic gene transfer

Leaflets from mature peanut embryos are a useful recipient tissue for biolistic DNA transfer. Fertile plants were regenerated from leaflets from genotypes representing all botanical types of peanut. Regeneration frequency was strongly influenced by genotype. NPT II and GUS chimaeric gene fusions, driven by the CaMV 35S promoter, were expressed transiently following biolistic delivery to unexpanded leaflets. Bombardment conditions affecting transient expression frequency were determined using a prototype of the Bio Rad PDS 1000/He helium-powered particle acceleration apparatus. Stably transformed calli were derived routinely from leaflet tissue bombarded with the NPT II gene and subsequently cultured on kanamycin. Several plants have been regenerated from treated explants under kanamycin selection. Thus far, none of these has been stably transformed. The occurrence of escapes suggests that kanamycin is an inefficient selective agent for the recovery of transgenic peanuts from this explant. Experiments designed to regenerate plants using published regeneration protocols from stably transformed calli, devoid of primary explant tissue, have been unsuccessful.     

Effect of soil sodicity on the growth,yield and chemical composition of groundnut (Arachis hypogaea Linn.)

Summary A replicated field experiment was conducted to study the effect of exchangeable sodium percentage (ESP) on the yield, chemical composition, protein and oil content and uptake of nutrients by groundnut (Arachis hypogaea Linn.) variety M-13. ESP over 15 delayed germination and emergence of flowers. There was continuous decrease in dry matter yield at 30 and 60 days of growth, grain and straw yield after harvest and protein, oil and kernel percent with increase in soil ESP. A 50 per cent reduction in groundnut yield was observed at an ESP of 20. Increasing soil ESP, increased Na and decreased K, Ca and N contents, but had no effect on the Mg, P, S, Fe, Mn, Zn and Cu contents of the plant. Sodium content of the plant increased, while potassium and nitrogen decreased with age of the plant. The uptake of all the nutrients decreased with increase in soil ESP. The results showed that groundnut is a relatively sensitive crop to soil sodicity.     

The influence of sucrose and an elevated CO2 concentration on photosynthesis of photoautotrophic peanut (Arachis hypogaea L.) cell cultures

Using photoautotrophic cells ofArachis hypogaea (L.) growing at ambient CO₂, it was shown that exogenous sucrose supplied to the liquid medium reduced¹⁴CO₂ fixation (supplied as NaH¹⁴CO₃). This was mostly due to a reduced labelling in P-esters, and to a lesser extent, in the serine/glycine moiety. However, radioactivity in the neutral sugar fraction was increased upon supplement of exogenous sucrose. The reduced labelling of P-esters and serine/glycine agrees with a lower concentration and specific activity of Rubisco in the sucrose supplied treatments as compared to the control. Following a transfer into a sugar free nutrient medium the concentration and activity of Rubisco is increased. The concentration of PEPCase was not influenced by sucrose application, although its specific activity was increased.At elevated CO₂ concentration (2.34% v/v) the Rubisco concentration and specific activity was at the same level as in the control (0.03% v/v CO₂). However, the concentration and the specific activity of PEPCase was increased and dry weight increase was about 8–9-fold higher than at ambient CO₂.     

Somatic embryogenesis from mature embryo-derived leaflets of peanut (Arachis Hypogaea L.)

Summary Embryogenic masses were obtained from immature leaves of peanut (Arachis hypogaea L.) cultured on a medium containing 20 mg/l 2,4-D. Somatic embryos developed from these masses following transfer to a medium containing 3 mg/l 2,4-D. The embryo morphology was quite variable. Following transfer to hormone-free medium, these embryos germinated. Shoot elongation was obtained in 25% of the embryos following transfer to a medium supplemented with 0.5 mg/l each of BAP and Kn. The plants grown in vitro by this method survived in sand:soil mixture and were grown to maturity.Abbreviations ABA abscisic acid - BAP 6-benzyl amino purine - 2,4-D 2,4 dichlorophenoxyacetic acid - GA₃ gibberellic acid - Kn kinetin - NAA 1-naphthaleneacetic acid - 2,4,5-T 2,4,5-trichlorophenoxyacetic acid - Z zeatin     

Quantification of the geocarposphere and rhizosphere effect of peanut (Arachis hypogaea L.)

Roots and pods of field-grown peanut (groundnut) (Arachis hypogaea L.) were sampled at the R3, R5, and R7 developmental stages and examined in comparison to root- and pod-free soil for microbial population densities to assess the geocarposphere and rhizosphere effects. G/ S (no. geocarposphere microorganisms/no. soil microorganisms) and R/S (no. rhizosphere microorganisms/no. soil microorganisms) ratios were calculated for total fungi,Asperigillus flavus, spore-forming bacilli, coryneform bacteria, fluorescent pseudomonads, and total bacteria isolated on low- and high-nutrient media. A clear geocarposphere effect was evidenced by increased population densities of bacteria and fungi associated with developing pods compared to soil. G/S and R/S ratios were generally greater than 1.0 for all groups of microorganisms except bacilli. G/S ratios were greater for total bacteria than for total fungi at two of the three sample times, suggesting that bacteria were stimulated more than fungi in the zone around developing pods. In contrast, R/S ratios, were higher for total fungi than for total bacteria at two of three sample times. The preferential association of fungi and bacteria with early developmental stages of the pod indicates that some microorganisms are particularly well adapted for colonization of the peanut geocarposphere. These microorganisms are logical candidates for evaluation as biological control candiates forA. flavus.     

Fractional changes in phenolic acids composition in root nodules of Arachis hypogaea L.

Phenolic acids are active antimicrobial compounds and root signaling molecules that play important roles in plant defense responses. They are generally present in plants as glycosides or esters. A range of soluble and bound phenolic acids were detected in roots and root nodules of Arachis hypogaea L., among which five were identified by high performance liquid chromatography (HPLC) coupled with UV–Vis diode array detector (DAD), viz., p-coumaric acid (p-com), p-hydroxybenzaldehyde (HBAld), p-hydroxybenzoic acid (HBA), caffeic acid (CA) and protocatechuic acid (PA). Para-coumaric acid was constitutively present in all fractions whereas HBA was present in the soluble form only in young nodules. CA and PA were mostly present in the wall bound fraction. The root nodules contain higher concentration of phenolic acids than non-nodulated roots and presence of peroxidase and polyphenol oxidase indicate the metabolism of phenolic acids in roots and root nodules. These results indicate that phenolic acids (p-com and CA) in bound-glycosidic or ester forms were major components in cell wall fortification which provide protection to the root nodule from pathogen attack.